Control device of refrigerating cycle, heat source device, and control method therefor

ABSTRACT

To provide a control device of a refrigerating cycle, a heat source device, and a control method therefor which are capable of realizing a stable low-load operation without using a hot gas bypass pipe. A centrifugal chiller includes a compressor compressing a refrigerant; a condenser condensing the refrigerant compressed by the compressor; an expansion valve expanding a liquid refrigerant delivered from the condenser; an evaporator evaporating the refrigerant expanded by the expansion valve; and a control device ( 10 ). The control device ( 10 ) includes a gas volume calculation unit ( 22 ) that calculates a current gas volume using a current actual cooling capacity; and a minimum gas volume calculation unit ( 23 ) that calculates a required minimum gas volume for the compressor using a parameter related to an operating condition of the compressor, in which if the current gas volume is less than the required minimum gas volume for the compressor, control is performed so as to increase an opening degree of the expansion valve.

TECHNICAL FIELD

The present invention relates to a control device of a refrigerating cycle, a heat source device, and a control method therefor.

BACKGROUND ART

In a heat source device such as a centrifugal chiller or an air conditioner having a refrigerating cycle, there is proposed, for example, a method for realizing a stable operation at a low load while securing a required minimum gas volume for a compressor by allowing a hot gas bypass pipe to bypass refrigerant gas from a discharge unit of a compressor or a condenser to an intake unit of the compressor or an evaporator (for example, PTL 1).

CITATION LIST Patent Literature

[PTL 1] Japanese Unexamined Patent Application Publication No. 2010-236833

SUMMARY OF INVENTION Technical Problem

However, it is necessary to the hot gas bypass pipe or a valve, thereby causing the size increase or cost increase of the device.

The present invention has been made in light of the problem, and an object of the present invention is to provide a control device of a refrigerating cycle, a heat source device, and a control method therefor which are capable of realizing a stable low load operation without using a hot gas bypass pipe.

Solution to Problem

According to a first aspect of the present invention, there is provided a control device of a refrigerating cycle including a compressor compressing a refrigerant, a condenser condensing the refrigerant compressed by the compressor, an expansion valve expanding a liquid refrigerant delivered from the condenser, and an evaporator evaporating the refrigerant expanded by the expansion valve, the control device including a gas volume calculation unit that calculates a current gas volume using a current actual cooling capacity; and a minimum gas volume calculation unit that calculates a required minimum gas volume for the compressor using a parameter related to an operating condition of the compressor, in which if the current gas volume is less than the required minimum gas volume for the compressor, the control device performs control so as to increase an opening degree of the expansion valve.

According to the configuration, if the current gas volume is less than the required minimum gas volume, the control device performs control so as to increase the opening degree of the expansion valve. Therefore, it is possible to deliver a gaseous refrigerant, the amount of which is greater than that of the refrigerant satisfying the cooling capacity, to the evaporator. As a result, it is possible to satisfy the demanded cooling capacity, and to realize a stable operation of the compressor at a low load.

The control device of a refrigerating cycle may further include a reference command calculation unit that calculates a reference opening degree command value in response to a demanded cooling capacity; a correction command calculation unit that calculates a correction opening degree command value in response to a difference between the current gas volume and the required minimum gas volume for the compressor; and an opening degree command value calculation unit that calculates an opening degree command value of the expansion valve by adding the correction opening degree command value to the reference opening degree command value.

According to the configuration, the correction command calculation unit calculates the correction opening degree command value in response to the difference between the current gas volume and the required minimum gas volume, and the opening degree command value calculation unit calculates the opening degree command value obtained by adding the correction opening degree command value to the reference opening degree command value. The opening degree of the expansion valve is controlled based on the opening degree command value. Therefore, if the current gas volume is less than the required minimum gas volume, along with the liquid refrigerant, the gaseous refrigerant required to secure the required minimum gas volume is delivered from the expansion valve to the evaporator. As a result, it is possible to satisfy the demanded cooling capacity, and to realize a stable operation of the compressor at a low load.

The control device of a refrigerating cycle may have opening degree command information in which an opening degree command value obtained by adding a correction opening degree command value for the required minimum gas volume for the compressor to a reference opening degree command value in response to a demanded cooling capacity is mapped to the demanded cooling capacity, and determine an opening degree command value corresponding to a currently demanded cooling capacity, from the opening degree command information.

According to the configuration, it is possible to easily acquire the opening degree command value satisfying both the demanded cooling capacity and the required minimum gas volume, by using the opening degree command information.

The refrigerating cycle may include an economizer provided between the condenser and the evaporator, and the expansion valve may include a first expansion valve provided between the condenser and the economizer and a second expansion valve provided between the economizer and the evaporator. Furthermore, in such configuration, if the current gas volume is less than the required minimum gas volume for the compressor, the control device of a refrigerating cycle may perform control so as to increase an opening degree of the first expansion valve and an opening degree of the second expansion valve.

According to such configuration, also in a double-stage compression type compressor, the first expansion valve and the second expansion valve can be controlled according to the opening degree command value satisfying both the demanded cooling capacity and the required minimum gas volume. Therefore, it is possible to realize a stable operation of the compressor at a low load.

According to a second aspect of the present invention, there is provided a heat source device including the control device of a refrigerating cycle.

According to a third aspect of the present invention, there is provided a method for controlling a refrigerating cycle including a compressor compressing a refrigerant, a condenser condensing the refrigerant compressed by the compressor, an expansion valve expanding a liquid refrigerant delivered from the condenser, and an evaporator evaporating the refrigerant expanded by the expansion valve, the method including calculating a current gas volume using a current actual cooling capacity; and calculating a required minimum gas volume for the compressor using a parameter related to an operating condition of the compressor, in which if the current gas volume is less than the required minimum gas volume for the compressor, control is performed so as to increase an opening degree of the expansion valve.

Advantageous Effects of Invention

The present invention provides the effect that it is possible to realize a stable low load operation without using the hot gas bypass pipe.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic configuration diagram illustrating a centrifugal chiller according to an embodiment of the present invention.

FIG. 2 is a functional block diagram of a control device according to the embodiment of the present invention.

FIG. 3 is a graph illustrating the relationship between a gas volume (∝ cooling capacity) and an opening degree command value (CV value) according to the embodiment of the present invention.

FIG. 4 is a graph for describing opening degree control for an expansion valve according to the embodiment of the present invention using the Mollier diagram of a refrigerant.

FIG. 5 is a schematic configuration diagram illustrating a centrifugal chiller according to another embodiment of the present invention.

FIG. 6 is a graph for describing opening degree control for an expansion valve according to the other embodiment of the present invention using the Mollier diagram of the refrigerant.

DESCRIPTION OF EMBODIMENTS

Hereinbelow, a control device of a refrigerating cycle, a heat source device, and a control method therefor according to an embodiment of the present invention will be described with reference to the drawings. In the following description, a centrifugal chiller is exemplified as the heat source device including a refrigerating cycle, but the present invention is not limited to this one example, and the heat source device may be an air conditioner, a water heater, or the like. A refrigerant applied to the refrigerating cycle is not specifically limited, but may be properly selected in response to the application or the like.

FIG. 1 is a schematic configuration diagram illustrating a centrifugal chiller 1 according to the embodiment of the present invention.

As illustrated in FIG. 1, the turbo chiller 1 includes a compressor 3 that compresses a refrigerant; a condenser 5 that condenses the high-temperature high-pressure refrigerant compressed by the compressor 3; an expansion valve 7 that expands the refrigerant delivered from the condenser 5; an evaporator 9 that evaporates the refrigerant expanded by the expansion valve 7; and a control device 10 that controls the centrifugal chiller 1.

The compressor 3 is, for example, a turbo compressor, and a centrifugal compressor is used as an example. The compressor 3 is driven by an electric motor 12, the rotation speed of which is controlled by an inverter 11. An output of the inverter 11 is controlled by the control device 10. In the embodiment, a variable speed compressor is exemplified, but a fixed speed compressor may be used.

An inlet guide vane (hereinbelow, referred to as “IGV”) 13 is provided at a refrigerant intake port of the compressor 3 to control a refrigerant intake flow rate, and is capable of controlling the capacity of the centrifugal chiller 1. The opening degree of the IGV 13 is controlled by the control device 10.

The compressor 3 includes an impeller rotating around a rotary shaft. A rotational power is transmitted from the electric motor 12 to the rotary shaft via a speed-increasing gear. The rotary shaft is supported by bearings.

The condenser 5 is a shell and tube type heat exchanger or a plate type heat exchanger. A coolant for cooling the refrigerant is supplied to the condenser 5. The coolant delivered to the condenser 5 is released to the outside in a cooling tower or an air heat exchanger which is not illustrated, and then is delivered back to the condenser 5.

The expansion valve 7 is an electric type. The low-temperature high-pressure refrigerant delivered from the condenser 5 is enthalpically expanded by the expansion valve 7. The opening degree of the expansion valve 7 is controlled by the control device 10 so as to be able to obtain a desired head difference (difference between the high pressure and the low pressure of the refrigerant in the refrigerating cycle).

The evaporator 9 is a shell and tube type heat exchanger or a plate type heat exchanger. Chilled water to be supplied to an external load (not illustrated) is delivered to the evaporator 9. The chilled water is cooled down to a rated temperature (for example, 7° C.) by exchanging heat with the refrigerant in the evaporator 9, and is fed to the external load (not illustrated).

The control device 10 is configured to include a central processing unit (CPU); a random access memory (RAM); a read only memory (ROM); a computer-readable storage medium; and the like. The control device 10 realizes various functions, as an example, by storing a series of processes for realizing various functions in the storage medium or the like in the form of a program (for example, control program), and causing the CPU to read the program into the RAM or the like and to process information and execute a calculation process. A form where the program is preinstalled on the ROM or other storage mediums, a form where the program is stored in the computer-readable storage medium and is provided to the control device, or a form where the program is transmitted to the control device via wired or wireless communication means may be applied. The computer-readable storage medium is a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, or a semiconductor memory.

FIG. 2 is a functional block diagram of the control device 10. As illustrated in FIG. 2, as main configuration elements, the control device 10 includes an expansion valve control unit 20 that controls the expansion valve 7, a reference command calculation unit 21, a gas volume calculation unit 22, a minimum gas volume calculation unit 23, a correction command calculation unit 24, and an opening degree command calculation unit 25.

The reference command calculation unit 21 calculates a reference opening degree command value in response to a demanded cooling capacity. The reference command calculation unit 21 calculates the reference opening degree command value (reference CV value) of the expansion valve 7, for example, from a target refrigerant circulation volume, which is calculated from the demanded cooling capacity, and a pressure difference between before and after the expansion valve 7. The target refrigerant circulation volume is calculated, for example, based on a required heat exchange amount required for the evaporator 9 to make a measured temperature value of the chilled water, which is supplied from the evaporator 9 to the external load, identical to a set temperature (for example, 7° C.). The reference opening degree command value of the expansion valve 7 is calculated from the pressure difference between before and after the expansion valve 7 so as to be able to obtain the target refrigerant circulation amount.

The gas volume calculation unit 22 calculates a current gas volume using a current actual cooling capacity.

The minimum gas volume calculation unit 23 calculates a required minimum gas volume for the compressor 3 using a parameter related to an operating condition of the compressor 3. More specifically, the minimum gas volume calculation unit 23 calculates the required minimum gas volume using a flow rate variable (cooling capacity) and a pressure variable (head) which indicate the operating condition of the compressor 3.

Well-known techniques may be employed for gas power calculation and minimum gas volume calculation.

The correction command calculation unit 24 calculates a correction opening degree command value (correction CV value) based on the current gas volume calculated by the gas volume calculation unit 22 and the required minimum gas volume calculated by the minimum gas volume calculation unit 23. Specifically, if the current gas volume is greater than or equal to the required minimum gas volume, the correction command calculation unit 24 sets the correction opening degree command value at zero, and if the current gas volume is less than the required minimum gas volume, the correction command calculation unit 24 calculates the correction opening degree command value in response to a difference between the current gas volume and the required minimum gas volume. For example, as the correction opening degree command value, the correction command calculation unit 24 calculates the difference between the current gas volume and the required minimum gas volume.

As the opening degree command value (CV value), the opening degree command calculation unit 25 calculates a value obtained by adding the reference opening degree command value (reference CV value) calculated by the reference command calculation unit 21 to the correction opening degree command value (correction CV value) calculated by the correction command calculation unit 24. Therefore, the opening degree of the expansion valve 7 is controlled based on the opening degree command value.

FIG. 3 is a graph illustrating the relationship between the gas volume (∝ cooling capacity) and the opening degree command value (CV value). As illustrated in FIG. 3, in a region where the gas volume is greater than or equal to the required minimum gas volume, the opening degree command value is set in response to the gas volume. Namely, the greater the gas volume is, the larger value the opening degree command value is set at. On the contrary, in a region where the gas volume is less than the required minimum gas volume, the less the gas volume is, the larger value the opening degree command value is set at. The reason is that the less the gas volume is, the larger the difference between the required minimum gas volume and the gas volume becomes, and thus the correction opening degree command value has a large value.

If the expansion valve 7 is controlled as described above, in the region where the current gas volume is less than the required minimum gas volume, as illustrated in FIG. 4, the refrigerant is depressurized by the expansion valve 7 in a two-phase gas-liquid phase region. Specifically, in the Mollier diagram of the refrigerant illustrated in FIG. 4, the refrigerant is depressurized in a state where the refrigerant has a specific enthalpy higher than a specific enthalpy point A corresponding to an intersection point between an isobaric line of an outlet pressure of the compressor 3 and a saturated liquid line.

Therefore, in the region where the current gas volume is less than the required minimum gas volume, along with a liquid refrigerant, a gaseous refrigerant required to secure the required minimum gas volume is delivered from the expansion valve 7 to the evaporator 9. As a result, it is possible to satisfy the demanded cooling capacity, to secure the gas volume greater than or equal to the required minimum gas volume, and to realize a stable operation of the compressor at a low load.

As described above, according to the control device of a refrigerating cycle, the heat source device, and the control method therefor according to the embodiment, if the current gas volume is greater than or equal to the required minimum gas volume, since the correction opening degree command value is to be set at zero, the opening degree of the expansion valve 7 is controlled based on the reference opening degree command value (=opening degree command value). However, if the current gas volume is less than the required minimum gas volume, the opening degree of the expansion valve 7 is controlled according to the opening degree command value obtained by adding the correction opening degree command value in response to the difference between the current gas volume and the required minimum gas volume to the reference opening degree command value. Namely, if the current gas volume is less than the required minimum gas volume, control is performed so as to increase the opening degree of the expansion valve 7 (refer to FIG. 3). Therefore, along with the liquid refrigerant, the gaseous refrigerant required to secure the required minimum gas volume is delivered from the expansion valve 7 to the evaporator 9. As a result, it is possible to satisfy the demanded cooling capacity, and to realize a stable operation of the compressor at a low load.

In the embodiment, a case where the reference command calculation unit 21 and the correction command calculation unit 24 calculate the opening degree command value in response to the demanded cooling load, the operating condition of the compressor, or the like on each occasion has been exemplarily described. However, the present invention is not limited to the example, but as illustrated in FIG. 3, opening degree command information in which the gas volume (∝ cooling capacity) is mapped to the opening degree command value (CV value) may be prepared in advance, and an opening degree command value corresponding to a currently demanded cooling capacity (gas volume) may be determined from the opening degree command information. In FIG. 3, the opening degree command value is an opening degree command value obtained by adding the correction opening degree command value for the required minimum gas volume for the compressor 3 to the reference opening degree command value in response to the demanded cooling capacity.

Another Embodiment

In the embodiment, a case where the compressor 3 with single-stage compression is used has been exemplarily described. However, as illustrated in FIG. 5, a centrifugal chiller 1′ may employ a double-stage compression type compressor 3′, and include an economizer 15 provided between the condenser 5 and the evaporator 9. Since other configuration elements are the same as those of the centrifugal chiller 1 illustrated in FIG. 1, the same reference signs are assigned thereto, and descriptions thereof will be omitted.

In the centrifugal chiller 1′ according to another embodiment, a first expansion valve 7 a is provided between the condenser 5 and the economizer 15, and a second expansion valve 7 b is provided between the economizer 15 and the evaporator 9. A gaseous refrigerant in the economizer 15 is supplied to an inlet side of a second-stage compressor. The valve opening degree of each of the first expansion valve 7 a and the second expansion valve 7 b is controlled by a control device 10′. Since a specific method for controlling the first expansion valve 7 a and the second expansion valve 7 b is the same as that of the embodiment, a description thereof will be omitted. As described above, controlling the expansion valve in the present invention can be applied also to a heat source device using the double-stage compression type compressor 3′, and a refrigerant state in the Mollier diagram of the refrigerant at that time has the trajectory illustrated in FIG. 6. FIG. 6 illustrates refrigerant characteristics when the current gas volume is less than the required minimum gas volume, in the Mollier diagram of the refrigerant when the double-stage compression type compressor 3′ is employed. As illustrated in FIG. 6, the valve opening degree of each of both the first expansion valve 7 a and the second expansion valve 7 b is controlled by the control device 10′ so as to depressurize the refrigerant in a two-phase gas-liquid phase region, namely, in a state where the refrigerant has a specific enthalpy higher than a specific enthalpy point B corresponding to an intersection point between an isobaric line of an outlet pressure of a first stage of the compressor 3′ and a saturated liquid line, and a specific enthalpy point C corresponding to an intersection point between an isobaric line of an outlet pressure of a second stage of the compressor 3′ and the saturated liquid line.

Therefore, the gaseous refrigerant required to secure the required minimum gas volume is delivered to the evaporator 9, and thus it is possible to satisfy the demanded cooling capacity, and to realize a stable operation of the compressor at a low load.

REFERENCE SIGNS LIST

-   -   1, 1′: centrifugal chiller     -   3, 3′: compressor     -   5: condenser     -   7: expansion valve     -   7 a: first expansion valve     -   7 b: second expansion valve     -   9: evaporator     -   10, 10′: control device     -   15: economizer 

1. A control device of a refrigerating cycle including a compressor compressing a refrigerant, a condenser condensing the refrigerant compressed by the compressor, an expansion valve expanding a liquid refrigerant delivered from the condenser, and an evaporator evaporating the refrigerant expanded by the expansion valve, the control device comprising: a gas volume calculation unit that calculates a current gas volume using a current actual cooling capacity; and a minimum gas volume calculation unit that calculates a required minimum gas volume for the compressor using a parameter related to an operating condition of the compressor, wherein if the current gas volume is less than the required minimum gas volume for the compressor, the control device performs control so as to increase an opening degree of the expansion valve.
 2. The control device of a refrigerating cycle according to claim 1, further comprising: a reference command calculation unit that calculates a reference opening degree command value in response to a demanded cooling capacity; a correction command calculation unit that calculates a correction opening degree command value in response to a difference between the current gas volume and the required minimum gas volume for the compressor; and an opening degree command value calculation unit that calculates an opening degree command value of the expansion valve by adding the correction opening degree command value to the reference opening degree command value.
 3. The control device of a refrigerating cycle according to claim 1, wherein the control device has opening degree command information in which an opening degree command value obtained by adding a correction opening degree command value for the required minimum gas volume for the compressor to a reference opening degree command value in response to a demanded cooling capacity is mapped to the demanded cooling capacity, and wherein the control device determines an opening degree command value corresponding to a currently demanded cooling capacity, from the opening degree command information.
 4. The control device of a refrigerating cycle according to claim 1, wherein the refrigerating cycle includes an economizer provided between the condenser and the evaporator, and the expansion valve includes a first expansion valve provided between the condenser and the economizer and a second expansion valve provided between the economizer and the evaporator, and wherein if the current gas volume is less than the required minimum gas volume for the compressor, the control device performs control so as to increase an opening degree of the first expansion valve and an opening degree of the second expansion valve.
 5. A heat source device comprising: the control device of a refrigerating cycle according to claim
 1. 6. A control method of a refrigerating cycle including a compressor compressing a refrigerant, a condenser condensing the refrigerant compressed by the compressor, an expansion valve expanding a liquid refrigerant delivered from the condenser, and an evaporator evaporating the refrigerant expanded by the expansion valve, the method comprising: calculating a current gas volume using a current actual cooling capacity; and calculating a required minimum gas volume for the compressor using a parameter related to an operating condition of the compressor, wherein if the current gas volume is less than the required minimum gas volume for the compressor, control is performed so as to increase an opening degree of the expansion valve. 